The invention relates generally to a multiple capacity gas-air mixing valve including an internal geometrical shape design for a tube-like gas-air mixing valve. The output of the valve is combusted in a downstream combustion device such as a boiler.
Related art gas-air mixing valve have particular inlet parts for gas-air mixing at particular capacities and drop pressures. These parts are typically designed by trial and error. For each trial, both inlet and outlet plastic parts, mounted in an aluminum body, have to be completely manufactured and tested, thus making the design process slow and expensive. Moreover, the efficiency of the resultant shape is not always satisfactory.
Most of the prior art relating to gas-air mixing relates generally to gas turbines, not to inlets for boilers. Spielman U.S. Pat. No. 5,611,684 relates generally to the field of use of the subject invention. In this patent, a gaseous fuel and combustion air are premixed. There is, however, no disclosure of a type mixing valve.
Leonard U.S. Pat. No. 5,257,499 employs a between the fuel introduction means and the air introduction means, such that the air flow is relatively constant over a large range of fuel flow rates. Both Mowill U.S. Pat. Nos. 5,477,671 and 5,572,862 disclose a having an inlet and an axis, where the inlet is operatively connect to the source of compressed air to define a compressed air flow path into the inlet. In essence these patents disclose the concept of using a separate from the combustion chamber to completely premix the fuel and air.
Forster U.S. Pat. No. 5,002,481 premixes heating oil by vaporization in steam rather than air. The vaporizing tubes of the second vaporizing portion have a smaller radius of curvature than the first as vaporization occurs in downwardly directed helical pipes. The resultant mix is discharged directly into a mixing space.
U.S. Pat. Nos. 4,845,952 and 4,966,001 (both to Beebe) also use tubes for mixing fuel by placing the tubes in the air flow path. These patents employ a multiple-venture tube pre-mix apparatus.
Hu U.S. Pat. No. 5,402,633 discloses a premix gas nozzle with a longitudinal tangential entrance slots. Kesseli U.S. Pat. No. 5,450,724 uses a plurality of mixing channels that are oriented to impart a swirling motion to the mixed combustion air and fuel. Finally, Booz U.S. Pat. No. 5,140,820 relates to a carburation system for small scale engines but is stated to be usable in larger engines and even auxiliary power units. It does not disclose a valve means.
The manufacturer of gas-air mixing valves is faced with a range of customers that is greatly diverse and requires a custom design for many of the boilers serviced by the valve manufacturer. With many boiler manufacturers and an almost unlimited number of applications for the boilers, the permutations of valve designs is equally immense. At the same time, each user of the boiler wants maximum efficiency, minimum pollution or unburned fuel, minimum cost and prompt, virtually immediate service and response to its demands for new valves.
The problem that exists is that a number of factors are important in the design process for making mixing valves. Previous to the present invention, valve parts were designed by experience, using trial and error methods that led to high design expense or less than optimum results. For each trial, both the inlet and outlet parts, which are made from plastic and mounted in an aluminum body, had to be completely manufactured and tested. This made the design process very slow and quite expensive. Moreover, the efficiency of the developed shape was not always satisfactory for the many different end uses.
Venture principle based gas-air mixing valves are employed in a multitude of boiler systems, particularly with industrial boilers that produce large quantities of energy for various industrial processes and applications. A large number of mixing valve characteristics need to be considered during the design of the valve. It is necessary to meet the requirements for air discharge, gas discharge, gas/air volume proportion for different fan loads, pressure drop along the valve, modulation band, maximal angle of the outlet part, and the like.
For example, in one industrial application where a large number of valves are produced, a pressure drop may range from less than 350 Pascals to more than 550 Pascals. at the same time, desired air capacities range from 18 to 66 cubic meters per hour (m.sup.3 /h) and the accompanying gas capacities for that range of air flow.
It would be of great advantage to provide a general inner shape profile for a gas-air mixing valve that would optimize the most important valve characteristics for a family of valves. These characteristics include gas/air volume proportion along different fan load, modulation band, which strongly determine valve overall efficiency.
It would be another great advance in the art if the required gas and air capacities could be accommodated by a valve having a particular shape profile for optimum results.
Another advantage would be if the outlet part of the valve would be configured to maximize the overall operation of the valve.
Other advantages will appear hereinafter.